Download transport of oxygen and oxygen-hemoglobin dissociation curve

TRANSPORT OF OXYGEN AND OXYGENHEMOGLOBIN DISSOCIATION CURVE
LEARNING OBJECTIVES
By the end of this lecture the students should be able to:
•
•
•
•
•
•
•
Explain the steps of gas exchange in lungs and tissue
Describe the process of oxygen diffusion
Explain the transport of oxygen in blood.
State the influence of oxygen on haemoglobin saturation.
Describe the role of haemoglobin in oxygen transport.
Explain the O2-Hb dissociation curve.
Describe the factors affecting on O2-Hb dissociation
curve.
Lecture outline
Overview of gas exchange
Oxygen exchange in lungs and tissues
• Diffusion through alveolar thin cells
• Down diffusion gradient
Higher in alveoli
Lower in blood
• Diffusion from blood to tissues
Also down gradient
First to ECF
Next to tissue cells
Oxygen transport in blood
Influence of PaO2 on hemoglobin
saturation
• 98% saturated arterial blood contains 20 ml oxygen per
100ml of blood (20 vol %)
• As arterial blood flow through capillaries , only 5 ml oxygen
are released
• Blood holds O2 reservoir
Structure of hemoglobin
Hemoglobin and its forms
• 4 peptide subunits ( 2 + 2) – globin combines with 4 molecules of
haem with Fe ++
• Hb A1 : 90 % of hemoglobin in adult
• Hb A2: 2 – 3 % hemoglobin in adult
• HbA1C : Glycosylated hemoglobin – an important marker to assess
the blood glucose control
• Hb F : 0.5% hemoglobin in adults – fetal hemoglobin , very high
affinity with oxygen
Role of hemoglobin in oxygen transport
• Each hemoglobin molecule combines with 4 oxygen
molecules in a rapid and reversible process
• The hemoglobin - oxygen complex is called as OXYHEMOGLOBIN
• Hemoglobin that has released oxygen is called as reduced
hemoglobin
Hemoglobin derivates unable to
transport O2
• Methhemoglobin : Contains Fe3+ instead of Fe2+
• Carboxy hemoglobin – contains CO instead of O2 (cherry
red in color)
• Sulfa – hemoglobin- contains sulfur – green in color
Oxygen –hemoglobin dissociation curve
Saturation of hemoglobin
• When all four haem are bound to oxygen , it is fully
saturated
98 % saturated in alveolar arteries
• When 1-3 haem molecules are bound to oxygen , then
hemoglobin is called as partially bound hemoglobin
Factor influencing hemoglobin saturation
• The rate at which hemoglobin binds and releases oxygen
depends on several factors:
1. Temperature
2. Blood pH
3. PCO2 level
4. 2,3-BPG
BPG modify the structure of hemoglobin , alters its affinity for
oxygenand enhances unloading.
2,3-bisphosphoglycerate
• Very important for long term regulation of Hb affinity with
O2
• 2,3-bisphosphoglycerate shunt is a pathway derived from
glycolysis
• Hypoxia stimulates 2,3 – BPG formation and thus improves
O2 release
Factor influencing hemoglobin saturation
• Right shift means higher ability to Hb to release oxygen but
lower ability to bind it
• Only 20- 25 % of bound oxygen is unloaded during one
systemic circulation
• If O2 level in tissues drops:
1. More oxygen dissociates from Hb and is used up by cells
2. Respiratory rate or cardiac output need not to be increased
Metabolic specialities of RBCs
•
•
•
•
No organelle – no mitochondria
Anaerobic glycolysis is the only source ATP formation
2,3- BPG shunt is unique for RBC
20% of glucose is metabolised via hexone
monophosphate pathway